There are various types of powder filling methods for filling up a container with the powder, such as a toner for electrophotographic printing, which include a rotary valve type, a screw feeder type and an auger type. The fundamental concept of these methods is to drop the powder by its gravity from the powder filling device to the container disposed under the powder filling device, so that the container is filled up with the powder.
Especially, the auger-type powder filling method is well known and put in practical use. This method is considered as an efficient method for filling up a container of a fixed capacity with the powder. See Japanese Laid-Open Patent Applications No. 04-087901 and No. 06-263101.
Immediately after the container is filled up with the powder by these powder filling methods, a certain amount of air is contained in the powder. In order that a large amount of powder is stored in a high-density state in the container for a short time, a powder filling method has been proposed. In this method, the suction pipe is inserted in the container and one end of the suction pipe is embedded in the powder in the container so that the air contained in the powder is reduced. See Japanese Laid-Open Patent Application No. 09-193902.
Usually, according to the auger-type powder filling method, the screw-like auger is provided inside the conical hopper near the outlet of the hopper, and the auger is rotated so that the toner within the hopper is discharged downward from the outlet. This procedure is carried out by filling the toner into one of the plurality of containers arranged and conveyed on the transport belt one by one.
In recent years, with respect to the image formation using the electrophotographic printing, there is the increasing demand for high-speed, high-clearness, high-quality image formation. With this trend, consideration is taken to the toner from the several standpoints: the average particle size of the toner is made to 10 micrometers or less, the fluidity is increased by applying metal oxide particles (the external additive) to the surface of the toner, and the low-temperature fixability of the toner is ensured by using a binding-agent resin of a low melting point.
However, the toner is pressurized by rotation of the auger in the case of the above-mentioned method, and the external additive of the toner will be separated or isolated from the surface. Furthermore, in the case of the auger type method, the external additive is buried in the toner, and the original function of increasing the fluidity by the external additive is eliminated or lost.
Moreover, in the case of the low-temperature fixing toner using a binding agent resin of a low melting point, the sticking of toner particles or aggregation is likely to occur since the toner is pressurized by rotation of the auger. Sometime the toner solidifies so that the aggregation does not return to the original state. As a result, the outlet of the hopper is clogged with the toner particles and the discharging is stopped. The problem that the toner filling work is interfered arises.
When the copying is performed with the developer in which the toner and the aggregation coexist, the quality of the reproduced image becomes inadequate since the aggregation has not a desired value of the electrostatic property.
The smaller the toner particle diameter is, the more the toner falls from the hopper to the container. The Brownian movement of such toner particles occurs in a gas regardless of the quality of the material. And it becomes easy to make an atomizing state. Then, the necessity of discharging a large amount of gas existing in the powder particles will arise, and it is difficult to form the high-density filling state of the toner in the container. It is desirable that the above-mentioned problem is solved to overcome such difficulty conjointly.
As described above, the auger type method requires a large-scale machine including the toner filling device having at least the hopper and the transport belt carrying and conveying the plurality of containers. And it is necessary that the container is arranged just below the toner filling device and filled up with the toner. Thus, the auger type method has the problem in that the arrangement of the toner filling device is fixed and several restrictions exist.
Another powder filling method has been proposed. In this method, gas is introduced to the powder filling device which stores the powder similar to the hopper, and the fluidity of the powder is increased. While the agitator is rotated, the powder from the outlet of the powder filling device is delivered to the container through the conveyance piping, and the gas existing in the powder particles is discharged through the de-aeration piping before the powder reaches the container. The objective of the proposed method is to supply the powder efficiently and filling up the container with the powder in a high-density state. See Japanese Laid-Open Patent Application No. 2001-031002.
However, the proposed method requires a large-scale powder filling device in which the de-aeration piping is accurately disposed co-axially with the powder filling piping. The manufacture of such powder filling device is difficult, and the weight becomes large.
Moreover, the powder filling device and the contained are disposed at separate locations. When a small-diameter container or a container in which the internal wall of the container is configured in the shape of a spiral convex or others is used in order to facilitate the toner discharging, the delivery of the powder is prevented and mixing the powder in the container with the air is difficult.
Moreover, since the de-aeration of the powder is performed in the course of delivery of the powder to the container, the delivery of the powder is difficult. Moreover, since the agitator is used to discharge the powder from the powder filling device, the separation of the external additive from the powder and the generation of aggregation will arise similar to the auger type method, and it is difficult to attain desired filling of the powder in the container.
Another powder filling method has been proposed. In this method, an auger-type powder filling device for filling a powder such as a medical supply or food into a container, such as a plastic bag. And the filter layer is provided in the cylindrical wall surrounding the auger connected with the lower part of the hopper, and the de-aeration of the gas existing in the powder is performed through the filter layer. By the de-aeration the negative pressure is generated, and the powder falling to the plastic bag by rotation of the auger is stopped. See Japanese Laid-Open Patent Application No. 2000-247445.
However, the proposed method uses the auger type method, and the above-mentioned problems still remain unresolved. In the case of the toner powder in which the external additive adheres, the separation of the external additive from the powder easily arises when the powder passes through the inside of the rotating auger. When the external additive whose particle diameter is smaller than that of the powder is attracted through the filter layer, clogging of the filter layer may occur, and it is difficult to attain appropriate stopping function of the filter layer.
In an office where an image forming device, such as a copier or a printer, is installed, when the developing unit of the device or the toner container is directly replenished with the toner, the particulate of the toner is produced. Even if it is replenished, the toner contains a certain amount of air and it is set in a low density state.
When the toner is supplied to the developing unit having a complicated structure directly, the filling state does not become uniform and the void is created so that the quality of the reproduced image becomes poor.
The inventors have proposed a powder fluidization unit for solving the above-mentioned problems in the toner filling method as disclosed in Japanese Patent Application No. 2001-102264.
The proposed powder fluidization unit is different from the auger type method mentioned above. In this powder fluidization unit, a minimum quantity of gas is introduced uniformly into the powder within the powder fluidization unit, and a fluidized state of the powder is acquired. After that, the powder in the fluidized state is supplied by pressurization into the container separated from the powder fluidization unit so that the container is filled up with the powder.
According to the above-mentioned powder filling method proposed by the inventors, it is possible to eliminate the separation of the external additive from the toner powder or the generation of the aggregation caused by rotation of the auger as in the auger type method. Moreover, the powder filling device is made small, carrying it is easy, the operation is easy, and it is very effective in eliminating the above-mentioned problems. Therefore it is possible to perform the filling of a small-inlet container or a complicated-shaped container with the powder sufficiently.
According to the above-mentioned powder filling method, the powder in the fluidized state, produced within the powder fluidization unit, can flow into the container through the transport pipe at high speed since it is fluidized and pressurized. The container can be immediately filled with the powder and the gas.
An important technical matter for filling each of the plurality of containers with the powder of the given quantity continuously one by one is to provide a controllable method so that the incoming flow is stopped instantly after one container is filled up with the powder of a given quantity, and the incoming flow can resumed for the following container so that the following container can also be filled up with the powder of the given quantity.
If that control cannot be performed enough, the powder is atomized around the powder filling device and the powder stain may occur. Although the inventors adjusted the pressure open valve provided in the above-mentioned conventional powder fluidization unit and controlled the delivery pressure, it is found that the feature of stopping the powder flow into the container instantly is inadequate.
It is conceivable that the cause of the above problem is that, because a certain time for escaping the air from the pressure open valve is needed, the falling of the residual pressure takes some time and the distance from the powder fluidization unit to the container is too long.
Moreover, the inventors provided the mechanical stop units, such as the valve or the shutter, at the edge of the powder filling nozzle being inserted into the container as the pressure control unit. As the filling operation is performed repeatedly, the aggregation of the powder is formed. It has been confirmed that the stop control of the powder filling is not performed adequately. It is conceivable that the cause of the above problem is that the powder is pressurized by the mechanical stop unit.